Streptococcus pneumoniae causes serious infections - pneumonia, meningitis, sepsis, arthritis and others in humans. It is also a causative agent in many less severe infections common in childhood, including otitis media and sinusitis. HIV infected children have a high incidence of bacterial pneumonia, otitis media and sinusitis, much of which is caused by pneumococcus, putting these children at particular risk for resultant bacteremia and serious sequelae of infection. Currently licensed polyvalent S. Pneumoniae does not induce an adequate antibody response in children less than two years old. In view of this, one potential method of reducing the risk to HIV infected children is to administer a pneumococcal conjugate vaccine (PCV) which is capable of producing an adequate antibody response in children less than two years of age, in concert with the requisite booster shots. ACTG 292 is a Phase I/II, double-blind, placebo-controlled, randomized, multi-centered trial to evaluate the safety and immunogenicity of a seven valent pneumococcal conjugate vaccine in sixty presumed HIV-infected infants 56-180 days old. Forty infants will be randomized to receive PCV and twenty infants will be randomized to receive placebo. To ensure adequate protection against infection, all children, regardless of treatment assignment will receive licensed pneumococcal polyvalent vaccine at two years of age, as in routine care. Primary objectives of this study are safety, tolerance, and immunogenicity, as well as duration of antibody protection against pneumococcal infection.